Geophysical prospecting system



y 1950 J. E. HAWKINS GEOPHYSICAL PROSPECTING SYSTEM 5 Sheets-Sheet 1 Filed Sept. 22, 1948 E5 35222 53 mm 8522mm x 32,529; tandem ZNVHVTOR. James E. Hawkins 95mm 22.5 55523 a .8 85

Filed Sept. 22, 1948 FIG. 3

J. E. HAWKINS 2,513,339

GEOPHYSICAL PROSPECTING SYSTEM 5 Sheets-Sheet 3 INVENTOR. James E Hawkins s m K w A H 5 Im GEOPHYSICAL PROSPECTING SYSTEM 5 Sheets-Sheet 5 Filed Sept. 22, 1948 kmomoumm ozSGomz M4505 u u oh mm 2K 32. 0% wmm w e 0 2 5.

ZNVEVTOR. James E. Hawkins Mans-n7 Patentecl July 4, i950 GEOPHYSICAL PROSPECTING SYSTEM James E. Hawkins, Tulsa, Okla., assignor to Seismograph Service Corporation, Tulsa, Okla", a corporation of Delaware Application September 22, 1948, Serial No. 50,493

attain '2 Claims. 3

The present invention relates to improvements in systems of geophysical prospecting and more particularly to an improved system for obtaining and correlating seismic data, position data and elevation data in conducting geophysical survey operations over land areas. This application is a continuation-in-part of applicant's copending application Serial No. 778,793, filed October 9, 1947.

In certain classes of geophysical prospecting operations, such, for example, as seismic pros pectin operations on land, it is necessary to obtain elevation data as well as survey point position data with a high degree of accuracy and to correlate this data with the seismic data in order to determine and record subsurface conditions of the earth. Conventional surveying methods are now universally used to obtain elevation and position data. Radio position finding systems have not been used for the reason that while reliably accurate systems for this purpose are known, no reliable system for utilizing radio waves to obtain elevation data has heretofore been available. Moreover, from the standpoint of actual operating practice using conventional surveying methods, it is practically as economical to obtain both elevation and position information as it is to obtain either type of information alone.

- Hence, radio systems of position determination have not been used to any appreciable extent in geophysical prospecting work.

It is an object of the present invention, therefore, to provide an improved system of geophysical prospecting in which position and elevation data are obtained radioelectrically without resorting to conventional manual survey methods.

It is another object of the present invention to provide a system of prospecting of the character described, particularly suitable for use in prospecting over land, in which position and elevation data and indications or signals representative of subsurface structural conditions are recorded on a common record element in a form which permits ready correlation and interpretation thereof.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawin s, in which:

Fig. 1 diagrammatically illustrates the fundamental arrangement of a survey system characterized by the features of the present invention;

Fig. 2 diagrammatically illustrates the equipment provided at the reference and elevation transmitter unit forming a part of the system shown in Fig. 1;

Fig. 3 illustrates the elevation signal wave transmitting antennas, the elevation and position signal wave collecting antenna and the relative positions of these antennas, as well as the family of isophase surfaces developed in space as a result of elevation signal wave radiation by the transmitting antennas; and

Figs. 4 and 5 when placed one above the other in the order named illustrate the mobile receiving unit forming a part of the system shown in Fig. 1.

Referring now to the drawings and more particularly to Fig. 1 thereof, the present improved system is there illustrated as comprising a plurality of geographically spaced apart broadcast transmitters til, it and i2 having radio antennas located at precisely known geographic locations, which commonly radiate program modulated carrier waves to an overlap area which includes an area 13 under survey. If the area it under survey is located in the western or central part of Michigan, for example, the broadcast transmitters employed in obtaining the desired position and elevation data may. comprise transmitter W'I'MJ located adjacent Milwaukee, Wisconsin, and operating at a carrier frequency of 620 kilocycles, transmitter WMAQ located adjacent Chicago, Illinois, and operating at a carrier frequency of 670 kilocycles and transmitter WJR located adjacent Detroit, Michigan, and operating at a carrier frequency of 760 kilocycles. These relatively high power transmitters are easily capable of reception at any reception point located within the central and western portions of the State of Michigan, using standard broadcast receivers. Assuming, therefore, that the prospect area l3 under survey is located in one of the western or central counties of Michigan, the program modu- .lated carriers radiated by the three identified transmitters may easily be received at all points within the area under survey at all times when the three transmitters are in operation.

For the purpose of utilizing the signals radiated by the three identified transmitters to provide position and elevation dataat a point located within the prospect area l3 under survey, a reference and elevation transmitter unit It and a mobile receiving unit l5 are provided. In conductin a given prospecting operation, the reference and elevation transmitter unit It may be set up at any desired location; preferably a location adjacent to or just within the border of the area to be prospected in order to reduce the power requirements of the transmitters embodied in the unit H and hence the likelihood of interference with other radio communication facilities operating in the same area. During operation of the system, the unit I4 is essentially a fixed position unit, although for purposes of transportation the components of the unit may be carried by a trailer which is hitched onto the vehicle carrying the components of the mobile receiving unit I 5. The latter unit may be moved to any desired position or point within the prospect area l3 under survey.

As specifically-described below, the transmitters l0, II and I2 continuously radiate amplitude modulated carrier waves having carrier components of diflerent frequencies, such that an interference pattern is formed in space to blanket the area under survey, all in a manner which will be fully apparent from the mathematical explanation appearing in Honore Patent No. 2,148,267, granted February 21, 1939. Three sets of hyperbolic isophase surfaces are thus' effectively produced in space by the carrier components of the waves radiated by the three transmitters. More specifically, the continuously radiated carrier wave components of the waves radiated by the transmitters I and II effectively produce an interference pattern characterized by a set of hyperbolic isophase surfaces having the radiation points of the transmitters i0 and II as foci. Each of these surfaces is representative of the loci of positions of constant phase difference between the carrier components of the waves radiated by the transmitters I 0 and il. Similarly, the signals radiated by the transmitters Ii and I2 provide a carrier wave interference pattern effectively characterized by a second set of hyperbolic isophase surfaces which transversely intersect the surfaces of the first set and have the radiation points of the transmitters ii and I2 as foci. The hyperbolic surfaces of the second set represent the loci of positions of constant phase difference between the carrier components of the waves radiated by the transmitters l I and 12. In the system arrangement herein disclosed, the third set of isophase surfaces produced in space by the carrier components of the signals radiated by the two transmitters i0 and 12 are not used. The manner of determining the effective spacing between the isophase surfaces is discussed more fully below. By heterodyning the carrier components of the signals radiated by the transmitters i0, II and 12 in pairs to produce resultant signals in the manner more fully explained below, the need for phase synchronization between the carrier components of the radiated signals is entirely obviated. For a mathematical analysis of the manner in which this is accomplished, attention is directed to the disclosure of the above cited Honore patent.

The equipment provided at the reference and elevation transmitter unit It serves the threefold function of converting the waves radiated from the transmitters H), II and I2 into position reference signals and transmitting these signals to the mobile receiving unit i5; generating elevation signals; and converting the generated elevation signals into' elevation reference signals and radiating the latter signals to the mobile unit i5. In brief and as best shown in Fig. 2 of the drawings, the equipment provided in the unit ll to develop the position reference signals comprises radio frequency selector and amplifier units It, l9 and 22 of conventional design for respectively receiving and amplifying the signals radiated by the transmitters H), II and I2; exceedingly narrow band pass filters I1, 20 and 22 for respectively passing the carrier components of the reproduced waves developed at the output sides of the selector and amplifier units II, II and 22 while rejecting the modulation components of these waves; a pair of mixers I2 and 2| for heterodyning the carrier wave components of the received signals in pairs to obtain sum and difference frequency signals; filters 24 and 2C for selectively passing the difference or beat frequency components of the heterodyned signals: and frequency dividers 25 and 21 for reducing the beat frequency signals to the desired frequency values. With this arrangement, the desired pair of position reference signals are developed acrossthe respective sets of output terminals of the frequency dividers 2B and 21.

For the dual purpose of transmitting the described position reference signals to the mobile receiving unit I! and of radiating elevation signals which blanket the area 12 under survey, a pair of ultra high frequency transmitters 28 and 29 are provided, which preferably are of limited power just suiilcient to permit adequate reception of the signals radiated thereby at all points within the survey area I! under all operating conditions. Each of the two transmitters 28 and 29 comprises an ultra high frequency master oscillator and a modulator and power amplifier unit and includes its own'individual antenna. Thus the transmitter 28 comprises a master oscillator 29a, designed to operate at a stable frequency of 152 megacycles, for example, a modulator and power amplifier unit 29b in which the position signal developed across the output terminals of the frequency divider 25 is amplitude modulated upon the carrier wave output of the oscillator 29a and an antenna 40 at which theposition signal modulated elevation signal developed by the transmitter 28 is radiated. Similarly, the transmitter 29 comprises a master oscillator 29a, designed to operate at a stable frequency of 152.1 megacycles, for example, a modulator and power amplifier unit 29b in which the position signal developed across the output terminals of the frequency divider 21 is amplitude modulated upon 'the carrier wave developed by the oscillator 29a and an antenna H from which the pmition signal modulated elevation signal developed by the transmitter 29 is radiated.

As stated above, facilities are also provided in the reference and elevation transmitter unit it for developing reference signals and transmitting the same to the mobile receiving unit 15. These facilities comprise radio frequency selector and amplifier units 92 and 35 for respectively receiving the signals radiated by the transmitters 29 and 29, narrow band pass filters 23 and 39 for passing the carrier wave components of the waves reproduced respectively by the units 32 and 22 while rejecting the modulation components thereof, a mixer 34, a filter 3'! for selecting the difference or beat frequency component of the heterodyned waves, a frequency divider 29 for reducing the selected beat frequency signal to the desired frequency value and a link transmitter 29 for transmitting the elevation reference signal to the mobile receiving unit it. The transmitter 99 is preferably of the low power, ultra high frequency, line-of-sight type and comprises a master oscillator 39a operated at a distinctive frequency of megacycles and a modulator and power amplifier unit 99b in which the elevation reference signal developed across the output terminals of the frequency divider 28 is amplitude modulated on the carrier wave output of the oscillator 39a, amplified and delivered to the antenna ground circuit of the transmitter 39 for radiation to the mobile receiving unit l5.

As indicated above, one of the functions assigned the transmitters 28 and 29 is that of producing elevation signals irom which may be determined the elevation of any survey point within the prospect area. 13 under survey. To this end, the antennas 40 and 4| of these transmitters are positioned at different known elevations above the earth's surface or more particularly above a known elevation datum plane. Thus and as best shown in Fig. 3 of the drawings, the antenna 48 is disposed above the antenna 4| in vertical alignment therewith and the two antennas are disposed different known or determinable distances above a point A of known elevation. The point A should have an elevation greater than the elevation of any surface point of the earth within the area under survey and the exact elevation of which may be determined by conventional surveying methods. Preferably, the facilities for supporting the antenna 4| are such that this antenna may be adjusted to an exact predetermined elevation DI above the point A. Similarly, the antenna 40 is preferably adjustable to a precisely determined elevation D2 above a the antenna 4|. The vertical space D2 between the two antenna 48 and 4| is preferably an integer multiple of the mean wavelength of the carrier wave components of the modulated signals radiated by the transmitters 28 and 29. Coaxial cables 42 and 43 are employed respectively to connect the antennas 40 and 4| to the antenna terminals of the modulator and power amplifier units 28?) and 291').

With the transmitters 28 and 29 in continuous operation, a set of hyperbolic isophase surfaces is produced in space through interference of the carrier wave components of the signals radiated by these transmitters. These surfaces represent the loci of positions of constant phase difference between the carrier components of the radiated waves and have the antennas 48 and 4| as foci. In any vertical plane bisecting the antennas 48 and 4|, the loci of points of constant phase difference between the radiated waves may of course be represented as hyperbolic lines in the manner shown in Fig. 3. Thus the hyperbolic lines 41 represent the loci of points of constant phase difierence between the carrier components of the radiated waves at points spaced laterally from the radiating antennas 40 and 4| disposed in a common vertical plane bisecting these two antennas. Obviously, by rotating this plane through 360, the isophase surfaces are developed. The manner in which this family of isophase surfaces is utilized in conjunction with the position signals radiated from the transmitters l0, II and I2 and the position reference signals radiated from the unit M to determine the eleva tion of any point within the area under survey and the efiective spacing between these surfaces i determined are explained more fully below.

From the above explanation, it will be apparent that three reference signal modulated carrier waves are radiated from the transmitters 28, 29 and 39 at the reference and elevation transmitter unit Hi to the mobile receiving unit l5 which may be located adjacent any survey point in the prospect area under survey. It is the purpose and function of the equipment provided in the mobile receiving unit I 5 to convert these received signals and those received directly from the transmitters III, II and I2 into indications representative of the position and elevation of a survey point at which the signals are collected. Briefly, and as best shown in Figs. 4 and 5 of the drawings, the equipment provided in the mobile receiving unit l5 to perform this function comprises wave receiving, translating, phase comparing and recording equipment, and wave collectors in the form of antennas 44a and 44b. As best shown in Fig. 3 of the drawings, the wave collecting antennas 44a and 44b are insulated from each other and ground and are carried by a mobile antenna support 46 consisting of a frame 46a and wheels 46b. The two antennas are disposed in vertical alignment and preferably are adjustable, within limits, to position theantenna 440 a desired elevation D3 above the survey point B on the earth's surface. From the antenna 44a the collected ultra high frequency waves are transmitted through a coaxial cable 45 to three ultra high frequency receiver 48, 49 and 58. Similarly, modulated carrier waves in the broadcast band collected by the antenna 44?) are transmitted over an insulated conductor 45b to the input terminals of three radio frequency selector and amplifier units 59, GI and 64. The receiver 48 is designed to accept the modulated 152 megacycle signal radiated from the transmitter 28 and comprises radio frequency selector and amplifier stages 50 followed by the usual converter, intermediate frequency selector, second detector and low frequency amplifier stages which are collectively indicated as being included in the block 5|. Similarly, the receiver 49 is designed to accept the modulated signal radiated by the transmitter 29 and comprises the usual radio frequency selector and amplifier stage 52 followed by the usual converter, intermediate frequency amplifier, second detector and low frequency amplifier stages collectively indicated as being included within the block 53. Portions 'of the signal voltages developed across the respective output terminals of the selector and amplifier stages 58 and 52 are impressed upon the input terminals of exceedingly narrow band pass filters 54 and 55 having the function of passing the carrier components of the selected waves and rejecting the modulation component of these waves. The carrier wave components passed by the filters 54 and 55 are heterodyned in a mixer 56 to produce sum and difference frequency signals in the usual manner, and the difference or beat frequency signal equaling that of the signal developed at the output terminals of the frequency divider 38 is selected by a filter 56a, frequency divided by a frequency divider 51 and impressed upon the upper set of input terminals of a phase meter I3 over the circuit conductors 51a. As explained more fully below, this signal is phase compared with the elevation reference signal transmitted to the mobile receiving unit l5 from the transmitter 38. More specifically, the receiver 58 performs the funct on of selecting and demodulating the modulated wave transmitted by the link transmitter 39 to reproduce the elevation reference signal acro s its output terminals. This reference signal is impressed across the lower set of input terminals of the phase meter I3 over the circuit conductors 58a.

The position reference signals respectively transmitted to the mobile receiving unit 15 from the transmitters 28 and 29 are selected, detected and amplified respectively in the stages 58 and 5| of the receiver 48 and the stages 52 and 53 of the receiver 48. Thus the position reference signal resulting from heterodyning. selecting and frequency dividing the carrier components of the signals radiated from the transmitters i and H at the reference and elevation transmitter unit M are reproduced across the output terminals of the receiver i8. Similarly, the position reference signal resulting from heterodyning, selecting and frequency dividing the carrier wave components of the signals radiated by the transmitters II and i2 at the reference and elevation transmitter unit H are reproduced across the output terminals of the receiver 49. These position reference signals are impressed respectively upon the lower sets of input terminals of the phase meters 12 and II over the circuit conductors 5m and 53a.

In order to develop "position signals at the mobile receiving unit ii for phase comparison with the position reference signals impressed upon the respective lower sets of input terminals of the phase meters I2 and H, facilities are provided in the unit [5 for directly receiving the signals radiated by the transmitters I0, I! and I2. More specifically, the signal originating at the transmitter H] is selected and amplified by the selector and amplifier unit '59 and delivered to an exceedingly narrow band pass filter 60 having the function of passing the carrier wave component of the signal while rejecting the modulation components thereof. Similarly, the radio frequency selector and amplifier unit 6| selects and amplifies the signal modulated carrier radiated by the transmitter H and transmits the same to an exceedingly narrow band pass filter 62 which passes the carrier component of the signal and rejects the modulation components thereof. The signal modulated carrier radiated by the transmitter I2 is selected and passed by the selector and amplifier unit GI and delivered to an exceedingly narrow band pass filter 65 which passes the carrier wave component thereof and rejects the modulation components. Thus the carrier wave components of the signals originating at the three transmitters Hi, If and I2 are received, selected, amplified and separated from the modulation components of these signals at the receiving unit l5. After such separation, the carrier waves developed at the output terminals of the filters 60 and 62 are heterodyned in a mixer 63 to produce the usual sum and difference frequency signals. The difference frequency signal is selectively passed by a filter 61, frequency divided by a frequency divider 68 and impressed upon the upper set of input terminals of the phase meter 12 over the circuit conductors 69a. Similarly, the carrier wave components of the signals originating at the transmitters H and I 2 as reproduced at the output sides of the filters 62 and 65 are heterodyned in a mixer 66 to produce the usual sum and difference frequency signals. The difference frequency signal is selectively passed by a filter 69, frequency divided by a frequency divider I0 and impressed upon the upper set of input terminals of the phase meter II over the circuit conductors a.

In accordance with the present invention, the indications produced by the three phase meters H, I2 and 13 along with seismic wave data are recorded upon a common record strip, thereby to facilitate interpretation and analysis thereof. To this end, a strip recorder 14 of the well known oscillographic type is provided, together with facilities for translating angular variations in the indicating needles of the three phase meters into current variations through the galvanometer trical degrees between two impressed signal voltages of the same frequency. Each phase meter is equipped with a rotor element carrying a pointer which indexes with a circular scale 'to indicate the phase relationship between the two impressed voltages. The rotor shafts of the three phase meters, indicated at 1B, and ,are also arranged to control the settings of six potentiometers I9, 92, 99, 9f, 91 and III! which govern the magnitude of current flow through six galvanometer coils 8|, 94, 90, 93, 99 and I02 of the recorder 14. More specifically, the rotor shaft I6 of the phase meter If is connected in driving relationship with the wiper 19a of the potentiometer 19 through reduction gearing comprising a pair of gears 1'! and 18. The resistor 19b of this potentiometer is arranged to be adjustably encircuited in the energizing circuit for the galvanometer coil 8| in series with an energizing battery 90. The purpose of providing the described facilities comprising the reduction gears 11 and 18, the potentiometer 19 and the battery to control the magnitude of current flow through the galvanometer coil If is that of permitting the recordation of data identifying a particular lane in which the wave collecting antenna 44 may be positioned or more particularly the particular pair of effective isophase lines of the family of isophase lines produced by the'transmitters I0 and II between which this antenna is disposed at any particular survey point B. Similar facilities comprising the reduction gears 88 and 81, the potentiometer 89 and the battery 99 are provided to control the magnitude of current flow through the galvanometer coil 90 in identical fashion, so that lane identification in respect to the position of the survey point B relative to the family of hyperbolic isophase lines produced by the signals radiated from the transmitters H and I2 is recorded on the record strip I5. Recordation of phase meter indications identifying the particular pair of effective isophase lines 41 between which the wave collecting antenna 44 may be disposed is accomplished by connecting the rotor shaft 94 of the elevation phase meter I3 through the reduction gears 95 and 96 to control the setting of the wiper 91a embodied in the potentiometer 91. The setting of this wiper obviously controls the magnitude of current flow from the enerizing battery 98 through the galvanometer coil 99.

In order to provide visual indications of the lanes in which the wave collecting antenna 44 is disposed, the shafts 18c, 81c and 960 rotated respectively by the large gears 18, 81 and 96 are respectively equipped with pointers 19a, 81a and 96a arranged to cooperate with scales 19b, 91b and 96b in producing the desired lane indications. Preferably, the scales 18b, 81b and 96b are each graduated in terms of lane width as determined by the transmitter operating frequen- 'ciated with these detectors.

fcies, so that the particular lanes in which the antenna 44 is disposed may be read directly by observing the positions of the pointers 18a, 81a and 300 relative to their respective associated scales.

In addition to controlling the operation of the recorder 14 in the recording of lane'identification information on the record strip 15, the three phase meters II, 12 and 13 are arranged to so govern the recorder that records are also produced on the record strip from which the particular phase settings of the rotor elements embodied in the three meters may respectively be determined. To this end, the shaft 15 is arranged directly to actuate the wiper 82a of the potentiometer 82 so that an adjustable portion of the potentiometer resistor 82b is encircuited with the galvanometer coil 84 in series with an energizing battery 83. Similarly, the rotor shafts 85 and 94 are arranged respectively to control the set-- tings of the two potentiometers 9| and I which govern the magnitudes of current flow from the batteries 92 and IOI through the galvanometer coils 93 and I02, respectively. Thus the phase meters II, I2 and I3 are arranged to produce a full and complete record identifying the position and elevation of the survey point on the record strip I5. In this regard, it is noted that the galvanometer elements in which the coils 8|, 84, S0, 93, 99 and I02 are respectively embodied individually control the positions of the record traces 8Ia, 84a, 90a, 93a, 99a and IBM transversely of the strip 15 or more particularly the vertical displacement of these traces from respective associated reference traces 8"), 84b, 90b, 93b, 99b and I02b.

The seismic wave detecting and translating equipment associated with the remaining galvanometer elements of the recorder I4 or a portion thereof comprises a plurality of seismic wave detectors, two of which are indicated at I03 and I04, and amplifying channels individually asso- In the arrangement illustrated, the detector I03 is connected to transmit detected seismic waves through an amplifier I05 to the galvanometer coil I01 of the recorder I4. Similarly, the detector I04 is arranged to deliver detected seismic waves through an amplifying channel I06 to the galvanometer element I08 of the recorder I4. It will be understood that any number of seismic wave detectors and associated amplifying channels may be employed in a given set-up within the limitation imposed by the available galvanometer elements of the recorder. It will also be understood that in an actual set-up, the detectors may be arranged in any desired arrangement relative to a shot point at which seismic wave generation occurs.

Where not otherwise specified in the foregoing description, the components of the described system are entirely conventional and well known in the art. It should be pointed out that the filters I1, 20, 23, 33, 38, 54, 55, 00, 62 and 65 are preferably of the crystal controlled type, each having a narrow pass band of the order of fifty cycles or less in width, such that all side band frequencies are substantially completely suppressed without undue attenuation of the carrier wave components. Filters of the type indicated having the desired narrow band pass characteristics are well known in the art. If found necessary to As previously pointed out with reference to Fig. 3 of the drawings, in setting up the equipment to perform survey work in the prospect area I3 under survey, the reference and elevation transmitter unit I4 is located at a high point preferably adjacent or within the boundary of the area. Further, the elevation of the earth's surface point A in vertical alignment with the two elevation transmitting antennas 40 and 4| is determined by conventional survey methods. These two antennas are adjusted to'the desired known elevations which will produce in space the vertically spaced hyperbolic isophase surfaces. More particularly, the two antennas are spaced apart an integer multiple of the wave length of the average frequency of carrier radiationby the two transmitters 20 and 29. Since the elevations of the two antennas 4| and 40 are known or may easily be determined from the known elevation of the surface point A, the actual elevation at any point within the system of isophase surfaces provided by the carrier waves radiated from these antennas may be determined when the position of the point laterally with respect to the transmitting antennas 40 and M is known. Determination of the position of the wave collecting point is effected by utilizing the two intersecting hyperboloidal systems of isophase surfaces produced in space by the carrier componeiits radiated by the three transmitters I0, II and 2.

Before describing the operation of the system, it should be pointed out that as viewed from the receiving and translating equipment provided at the mobile unit or station I5, the effective spacing between the hyperbolic isophase surfaces produced by the carrier waves radiated by each pair of transmitters I0I I, III2 and 28-49 is that which will produce 360 degrees of rotation of the rotor element in the phase meter II, I2 or I3 which responds to the carrier waves radiated by the particular pair of transmitters when the collecting antennas 44a and 44b are moved across the interference pattern produced by these carrier waves. This effective spacing is determined by two factors, namely, the mean frequency of the carrier waves radiated by the pair of transmitters and the extent to which the beat frequency signal produced by heterodyning these carrier waves at the stations I4 and I5 is frequency divided at these stations to obtain the signals which are phase compared at the station l5. More specifically, the effective isophase surface spacing as measured along the base line between the radiation points of a particular pair of transmitters is equal to one-half the wave length corresponding to the mean frequency of the carriers radiated by the two transmitters multiplied by the factor used in frequency dividing the beat frequency signalobtained by heterodyning the two carriers at the stations I4 and I5. In the illustrated system arrangement, each of the three beat frequency signals developed at each of the stations I4 and I5 is frequency divided by a factor of ten. Accordingly and considering the pair of elevation position signal transmitters 28 and 29 by way of example, the effective spacing between the isophase surfaces resulting from carrier wave radiation by these transmitters as measured along the vertical line connecting the antennas 40 and M, is five times the wave length corresponding to the mean carrier frequency of 152.05 megacycles, i. e., approximately ten meters. At points laterally displaced from this vertical line, the effective spacing between the equiphase v 11 is greater due to the hyperbolic contour of the surfaces. rmconvenience of explanation, it is assumed that the isophase lines "shown in Pig. 8 of the drawings are spaced in accordance with the effective spacing described above, i. e., tely ten meters along and ll.

In the operation of the abov described system, it will be understood that at any location of the mobile receiving unit it and more particularly the wave collecting antennas a and b within the radius of tron of the transmitten II, II, II, 2|, 2! and 38, the equipment provided in the mobile receiving unit is arranged to provide-three phase indications which definitely locate the position of the collecting antennas and the elevation of the antenna a above the survey point. The survey points may comprise the location of shot holes and the locations of the seismic wave detectors arranged in a given array relative to a particular shot hole. More in detail, the amplitude modulated signal radiated ,by the transmitter I8 is selected and amplifiedat the unit I by the selector and amplifier stages I I and the 620 kilocycle carrier wave component is selectively to the exclusion of the modulation components by the band pass filter II and impressed upon the upper set of input terminals of the mixer l8. Similarly, the selector and amplifier unit 22 and the band pass filter 23 function to separate the 760 kilocycle carrier wave component of the signal radiated by the transmitter l2 and to impress this carrier wave upon the lower set of input terminals of the mixer 2i. The selector and amplifier unit It and the band pass filter 28 separate the 6'70 kilocycle carrier wave component from the signal radiated by the transmitter II and impress this carrier wave upon the respective upper and lower sets of input terminals, respectively, of the two mixers 2| and I8. The mixer It operates to produce the usual sum and difference frequency signals across its output terminals when energiaed by the 6'10 and 620 kilocycle input signals. However, only the difference frequency signal of 50 kilocycles as developed across the output terminalsofthemixer llispassedbythefilterfl. ,This 50 kilocycle signal is frequency divided by a factor of ten through operation of the frequency divided 2! which may comprise one or more stages, such that a kilocycle signal is developed at the output terminals of the frequency divider for modulation upon the 152 megacycle carrier wave radiated by the transmitter 28. In a similar manner, the 8'10 kilocycle and 760 kilocycle carrier waves developed at the respective output sides of the filters 28 and 28 are heterodyned in the mixer 2| to produce a 90 kilocycle difference frequency signal which is selectively passed by the filter 28 and frequency divided by a factor of ten through operation of the frequency divider 21 to produce a 8 kilocycle signal. This signal is modulated upon the 152.1 megacycle carrier wave radiated by the transmitter 28.

When the illustrated system arrangement is med, the two position reference signal modulated carrier waves radiated by the transmitters 28 and 28. are respectivelyreceived and amplified by the selector and amplifier units 32 and It. The carrier wave components of the selected waves are passed by the two filters 83 and 38,-heterodyned in the mixer 84 to produce a difi'erence frequency signalof one hundred kilocycles which is reduced to a frequency of 10 kilocycles through operation 12 of the frequency divider 88 and impressed upon the 170' megacycle carrier wave output of the transmitter 38 for radiation to the mobile receivins unit It. a

From the preceding explanation, it will be apparent that five distinct and useful signals are radiated from the reference and elevation transmitter unit It to the mobile receiving unit It even though only three transmitters are provided at the reference and elevation unit. This is accomplished by employing the transmitters 28 and 28 in the dual capacity of elevation signal transe170 megacycle carrier wave modulated with a 10 kilocycle component which is used as an elcvation reference signal.

At the mobile receiving unit It, the ultra high frequency waves radiated from the three transmitters 28, 28, and 39 are collected by the antenna a and'transmitted over the coaxial cable to to the input terminals of the three receivers 48, 4s and 58. Similarly, the relatively low frequency waves radiated by the transmitters III, II and I2 are collected by the antenna b and transmitted over the conductor 45b to the three radio frequency selector and amplifier units 58, ii and 64. The radio frequency selector and amplifier section 50 of the receiver 48 selects the modulated 152 megacycle signal radiated by the transmitter 28, and the 5 kilocycle position reference signal component of the selected wave is detected and reproduced by the succeeding stages of the receiver 48 and impressed uponthe lower set of input terminals of the phase meter I2 over the circuit conductors 5 la. Similarly, the modulated 152.1 megacycle wave radiated by the trans-' mitter 28 is selectively passed and amplified by the selector and amplifier section 82 of the re- A ceiver 48 and the 9 kilocycle position reference signal component of this wave is reproduced by the succeeding stages of the receiver is and applied to the lower set of input terminals of the phase meter H over the. circuit conductors Ila. The 9 and 5 kilocycle position signals which are phase compared with the described position reference signals of like frequencies are developed locally at the mobile receiving unit II. To this end, the modulated 620, 670 and 760 kilocycle signals radiated by the transmitters in, II and I2 are respectively selected by the radio frequency selector and amplifier units 59, 6| and 64 for carrier wave filtering by the narrow band pass filters 68, 62 and 65. Thus the 620 kilocycle and 670 kilocycle carrierv wave components of the 13 c the 50 kilocycle filter 51 and frequency divided by a factor of ten in the frequency divider 58 to produce a 5 kilocycle position signal which is impressed upon the upper set of input terminals of the phase meters 12 over the circuit conductors 68a. In an identical manner, the mixer 65 functions to heterodyne the 670 and 760 kilocycle signals to produce sum and difierence frequency signals. The difference frequency signal of 90 kilocycles is selectively passed by the filter 59 and frequency divided by a factor of ten in the frequency divider Ill to produce a 9 kilocycle position signal which is impressed upon the upper set of input terminals of the phase meter ll over the circuit conductors 10a.

The 10 kilocycle elevation reference signal modulated on the carrier wave radiated by the transmitter 39 is detected and reproduced by the receiver 58 for application to the lower set of input terminals of the phase meter 13 over the circuit conductors 58a. An elevation signal is also developed locally at the mobile receiving unit I5 by heterodyning the carrier wave components of the waves radiated by the transmitters 28 and 29. To this end, a portion of the signal voltage appearing at the output side of the selector and amplifier section 50 ofthe receiver 48 is impressed upon the input terminals of the band pass'filter 54 which functions to pass the 152 megacycle carrier wave component and to reject the 5 kilocycle modulation component. The carrier wave component selected by the filter 54 is impressed upon the lower set of input terminals of the mixer 56. Similarly, a portion of the signal voltage appearing at the output side of the radio frequency section 52 of the receiver 49 is impressed upon the input terminals of the band pass filter 55 with the result that the 152 megacycle carrier wave component of the signal voltage is passed by this filter for application to the upper. set of input terminals of the mixer 56. This mixer functions to heterodyne the two signals with the result that the usual sum and diflerence frequency signals are developed across the output terminals thereof. The one hundred kilocycle difference frequency signal is selectively passed by the filter 56a and frequency divided by a factor of ten through operation of the frequency divider 51 to produce a 10 kilocycle elevation signal which is impressed upon the upper set of input terminals of the phase meter 13 over the circuit conductors 51a.

When thus energized by the two input signals of like frequency, i. e., 10 kilocycles, which may have a phase displacement ranging from zero to more than 360, the rotor element of the phase meter 13 assumes a setting precisely representative of the phase angle between the two signal voltages and hence provides an indication of the position of the wave collecting antenna 44a relative to two of the isophase lines 41. As noted above, with the described arrangement, wherein elevation signals having frequencies of 152 and 152.1 megacycles are heterodyned, the effective spacing between the isophase surfaces produced in space and hence the isophase lines 41 is in part determined by the mean frequency of 152.05 megacycles between the two elevation signal frequencies and in part by the factor of ten used in frequency dividing the beat frequency signals in the frequency dividers 38 and 51. Using the values given, the isophase lines 41 representative of the same phase relationship between the standing waves are effectively spaced apart vertically a minimum distance of-about 10 meters along the vertical line extending through the antennas 40 and 4| and an increasingly greater distance at lateral points increasingly distant from this vertical line. Hence the indication provided by the phase meter I3 identifies the position of the wave collecting antenna 44a within a vertical zone having a minimum width of about 10 meters. Specifically, the indication providedby the meter 13 shows the position of the wave collecting antenna in terms of the vertical distance of this antenna from each of the two ad- .iacent isophase lines 41a and 41b. Further, the position of the indicating needle a relative to the lane scale 96?) identifies the particular pair of isophase lines between which the wave collecting antenna, 44a is disposed. Thus the phase meter 13 in cooperation with the scale and pointer assembly actuated by this meter functions to provide an indication of the exact location of the antenna 44a relative to a particular pair of isophase lines 41a and 4'"). However, these facilities do not alone indicate the position of the antenna 44a relative to the transmitting antennas 40 and 4| and hence do not alone indicate the elevation of the survey point B. Positional information is supplied by the phase meters H and 12 which identify the geographic location of the survey point B.

At this point it may be noted that if the beat frequency signals are frequency divided by a factor of ten in the manner described and the vertical spacing between the antennas 40 and 4| equals five times the wave length of a wave having a frequency equaling the mean frequency of the elevation signals, only two isophase surfaces are effectively produced in space and hence the total indicating range of the phase meter 13 is 360. Thus if the transmitters are operated at the indicated carrier frequencies of 152 and 152.1 megacycles such that the mean carrier frequency is 0.1 megacycle, the beat frequency signal therebetween is divided by ten, and the antennas 40 and 4| are spaced apart a distance of approximately 10 meters, the total 360 indicating range of the phase meter 13 covers a vertical distance range of approximately thirty-three feet at the antennas and ranging upward from this distance at points spaced laterally from the transmitters. An arrangement of this character obviously makes it possible to omit the lane identification apparatus comprising the elements 95, 96, 96a, 96b, 96c, 91 and 98 from the indicating and recording equipment.

As will be partially apparent from the foregoing explanation, the phase meter 1| responds to the two 9 kilocycle position and position reference signals derived from the carrier wave components radiated by the transmitters II and I2 to produce an indication of the position of the wave collecting antenna 44b relative to the hyperbolic surfaces defining the loci of constant phase difference between the standing waves produced in space by the carrier wave components of the signals radiated by the 'two identified transmitters. In this case, wherein the mean carrier wave signal frequency of thetwo signals originating at the transmitters II and I2 is 715 kilocycles and the beat frequency signals are each frequency divided by ten, the effective spacing between the isophase surfaces is approximately 6880 feet along the base line connecting the radiating antennas of these two transmitters and greater at positions on either side of this base line. Hence theindication provided by the phase meter ll identifies the position of the antenna b within a zone having a minimum width equal to five times the wave length of the mean frequency signal or 6880 feet. Further, the indicating needle 81a in cooperation with the lane identification scale 81b function to identify the particular pair of isophase surfaces between which the antenna b is disposed.

In a similar manner, the phase meter I2 responds to the 5 kilocycle position and position reference signals derived from the carrier wave components of the signals radiated by the transmltters In and II to provide an indication representative of the position of the wave collecting antenna b relative to-a particular pair of hyperbolic isophase surfaces produced in space by the carrier wave components of the signals radiated from the two identified transmitters. This indication is likewise based on the mean frequency of 645 kilocycles between the carrier wave frequencies of the signals radiated by the two transmitters l and II and the factor of ten used in frequency dividing the beat frequency signals and is equal to 7630 feet. Here also, the indicating needle 18a in cooperation with the associated lane identification scale 18b identifies the particular pair of isophase surfaces between which the antenna b is disposed.

From the preceding explanation, it will be understood that the three phase meters ll, 12, and 13 in cooperation with the associated lane identification scale and pointer assemblies function to provide indications which when correlated specifically identify the position of the antennas a and b relative to the known positions of the transmitters III, II and I2 and also the elevation of the antenna a relative to the known elevations of the transmitting antennas 40 and 4|. Further, location of the position of the antenna a relative to the known positions of the transmitters l0, Ii and i2 definitely fixes the geographic position of this antenna. Once this position is known, the elevation of the antenna a may readily be determined by consulting hyperbolic charts prepared to show the effective isophase lines produced in space by the waves radiated from the antennas ill and 4| by the transmitters 28 and 29. Once the elevation of the antenna a, relative to the known elevation of the antennas 40 and 4| is thus determined, it is a simple matter to determin the elevation of the survey point B by subtracting the distance D3 from the indication elevation of the antenna a. To summarize, the phase meters 1 I l2 and 13 provide indications which definitely fix in three dimensions the position of the wave collecting antenna a in space and hence identify the geographic position of this antenna as well as the elevation thereof relative to a known datum elevation such, for example, as sea level.

As described above, the rotatable indicating elements of the three phase meters H, 12 and 13 are arranged to control the settings of the six potentiometers I9, 82, 88, 9|, 91 and HID. Hence as the settings of the phase meter indicating elements are changed, the magnitudes of current fiow through the respective asociated galvanometer coils BI, 84, 90, 93, 99 and I02 are correspondingly changed to produce corresponding changes in the settings of the galvanometer mirrors respectively associated with these coils. Thus the system is so arranged that the six indications necessary to determine in three dimensions the osition of the wave collecting antenna a. in space may be recorded by the recorder 16 signals developed during a seismic shootin operation.

The manner in which the seismic wave detectors IDS-4M are arranged in a predetermined array relative to a shot point and function to convert into electrical signals the reflected and refracted seismic waves resulting from detonation of an explosive charge at the shot point will be readily understood by those skilled in the art of seismic surveying. In the usual case, the explosive charge is detonated beneath the surface of the earth at a known position displaced a predetermined distance from the detector array, and the detectors are likewise displaced from each other predetermined distances and arranged in a definite array, such, for example, as in line with the shot point. The described system may be employed for the purpose of definitely determining the position and elevation of the shot point as well as the position and elevation of each detector location point in the detector array, all in a manner which will be fully apparent from the foregoing explanation. Specifically, the mobile unit l5 may be moved from point to point to locate the antennas a and b directly over difi'erent survey point; B at which the shot point and each detector placement point are located.

As the shot and detector oints are successively located, the recorder 14 may be successively operated to produce a series of record indications on the recording strip 15 which may be easily interpreted definitely to identify the geographic location and elevation of each of the points. In this regard it will be understood that during each operation of the recorder ll, each galvanometer element produces a separate and distinct trace on the record strip I5 and theposition of the trace transversely of the strip follows variations in the energization of the galvanometer coil embodied in the element. Thus as the galvanometer coil ii is variably energized under the control of the potentiometer 19 during a given recording operation, a trace 8la is produced on the record strip which follows variations in the energization of the coil 8| Since, however, at any given location on the antenna a, the coil 8| is constantly energized by current having a constant magnitude related to the setting of the lane identificaion needle 1811, a straight line trace ii a is produced on the record strip 15 during the recording operation. The distance between this trace and the reference line 8lb, representative of zero energization of the coil BI, is accurately indicative of the particular pair of isophase lines 41 relative to which the antenna a is disposed. Further, the setting of the potentiometer 82 as determined by the angular position of the rotor element in the phase meter H establishes a given- 13 cause straight line traces a, 93a, 89a and 102a to be produced on the record strip 15 during each recording operation which are respectively spaced from their associated reference lines 902) 9315.! and'lMb by distances accurately in-' dicative of the lane and phase indications provided by the two phase meters and their respective associated scale and pointer assemblies. 4

Thus by operating the recorder 14 for a very short interval as each shot and detector point is 40 on the same record strip 15 as the seismic 1 located. a pictorial record is produced on the 17 record strip 15 which may readily be interpreted to provide all of the necessary position and elevation information regarding the set-up made prior to a shooting operation.

After the explosive charge is located at the shot point and the detectors I03-l04 are located in the proper positions relative to the shot points, the explosive charge may be detonated in the usual manner to propagate seismic waves through the subsurface structure of the earth. These waves are reflected and refracted from strata interfaces and the like to be detected by the detectors I03l04. The detected waves are converted into corresponding electrical signals by the detectors l03l04 in the usual manner and these signals are amplified by the amplifiers lB5-l06 and impressed upon the galvanometer coils lfll-I08 of the recorder 14. This recorder is operated continuously during the shooting op eration so that record traces I 01a-l08a are produced on the record strip 15 which pictorially depict the detected seismic waves. Concurrently with recording of the seismic wave trains picked up by the detectors IB3-IM, the traces Bla, 84a, 90a, 93a, 99a and IBM are again produced on the record strip to identify the location of the wave collecting antenna 44a during the shooting operation. After the record is thus completed, it may be severed from the record strip supply roll, developed and interpreted, with all of the necessary information regarding the geographic locations and elevations of the shot and detector points being portrayed on the same record on which the seismic information is recorded.

While one embodiment of the invention has been described, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a system of geophysical prospecting, recording apparatus including means for driving a movable record element, prospecting apparatus including means for activating said recording apparatus to produce a record on said record element representative of a characteristic of the earths subsurface structure, radio elevation finding apparatus, and means responsive to operation of said elevation finding apparatus for governing said recording apparatus to produce a record on said record element of the earths elevation at the location at which said first-named record is produced on said record element.

2. In a system of geophysical prospecting, recording apparatus including means for driving a movable record element, prospecting apparatus including means for activat ng said recording apparatus to produce a record on said record element representative of a characteristic of the earths subsurface structure, radio position and elevation finding apparatus, and means responsive to operation of said position and elevation finding apparatus for governing said recording apparatus to produce records on said record element indicating the location at which said firstnamed record is produced on sa d record element and the earths elevation atsaid location.

3. In a system of geophysical prospecting, recording apparatus including means for driving a movable record element, prospecting apparatus including means for activating said recording apparatus to produce a record on said record element representative of a characteristic of the earths subsurface structure, radio position finding apparatus, means responsive to operation of said position finding apparatus for governing said recording apparatus to produce a, record on said record element of the geographic location at which said first-named record is produced on said record element, radio elevation finding apparatus, and means responsive to operation of said elevation finding apparatus for governing said recording apparatus to produce a separate record on said record element of the earths elevation at said location.

4. In a system of geophysical prospecting, prosspecting apparatus including means for producing an electrical signal representative of a characteristic of the earths subsurface structure, radio elevation finding apparatus including means for producing an electrical signal at least partially representative of earths elevation above said subsurface structure, and recording means responsive to said first and second-named signals for recording said signals on a common record element.

5. In a system of geophysical prospecting, prospecting apparatus including means for producing an electrical signal representative of a characteristic of the earths subsurface structure, radio elevation finding apparatus including means for, producing an electrical signal at least partially representative of earths elevation above said subsurface structure, radio position finding apparatus for producing an electrical signal at least partially representative of the geographic location of said subsurface structure, and-recording means responsive to said signals for recording said signals on a common record element.

6. In a system of geophysical prospecting, a recorder including record producing elements adapted to be separately activated to produce separate records on a common record element, prospecting apparatus including means for activating one of said elements in accordance with a signal representative of a characteristic of the earths subsurface structure, and radio elevation finding apparatus including means for activating another of said elements in accordance with a signal at least partially representative of the earths elevation at a point above said subsurface structure.

'7. In a system of geophysical prospecting, a recorder including record producing elements adapted to be separately activated to produce separate records on a common record element, prospecting apparatus including means for activating one of said elements in accordance with a signal representative of a characteristic of the earths subsurface structure, radio elevation finding apparatus including means for activating another of said elements in accordance with a si nal at least partially representative of the earths elevation at a point above said subsurface structure, and radio position finding apparatus in--" cluding means for activating still another of said elements in accordance with a signal at least partially representative of the geographic location of said point.

JAMES E. HAWKINS.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,706.066 Karcher Mar. 19, 1929 1,843,725 Karcher Feb. 2, 1932 2,148,267 Honore Feb. 21, 1939 

